Many actors talk of films being life-changing experiences. With Life of Pi, Mr Suraj Sharma has had his entire existence flipped, transformed, turned upside down and inside out. Before he was cast at the age of 17, he'd never acted; he couldn't swim; he'd never left India. He grew up in suburban South Delhi, the son of an economist mother and a software engineer father. He was at school, half-heartedly training to be an economist when his younger brother asked him to accompany him to the Life of Pi auditions, as he didn't want to go on his own. The casting director told him he might as well try out too. Three years on, he finds himself in a position of global acclaim and stardom, his life a constant stream of premieres, promotions and parties. Not that you'd know it. He's a wonderfully relaxed, playful model at our shoot, humble and charming, with no sign of the eternal jet lag he's enduring. Cast from 3,000 hopefuls, it's clear what Mr Ang Lee saw in him - his gentle, lovely spirit matches that of the film. Currently studying philosophy at Delhi University, he's taking things slowly and says he may not act again. Whatever he does with his life, it's sure to be something great.

Do you think it worked in your favour that you weren't an actor?

Yeah. Ang said the fact that I wasn't trained allowed him to mould me into whatever he wanted. So I was trying to find my way out as the story moved along. I was acting; my character was trying to survive. But we were both going into the unknown, trying to figure out what needed to be done.

I read on the second audition you did with Mr Lee that you started crying. What happened?

He talked to me in a certain way, put me in a state of mind. You take him seriously whenever he speaks. He's very soft-spoken so you're trying to listen even harder, you end up concentrating a lot. And he's trying to make you understand that you basically need to find the same emotion as the character. You don't need to be in the same spot, but being in that emotional state, inside you are in the same spot, in some senses. So that's what he did. And it was a long scene. The emotion built up and up and up to the point where crying seemed appropriate.

For a month Ang told everybody not to talk to me, so I'd have complete isolation. I was just meditating on my own or going through this super crazy work-out

I read that in order to look emaciated in the film, you were on a tuna and lettuce diet for three months. Did you pig out when you got off it?

I couldn't, I still can't really. My stomach's shrunk. When I was 14 I could eat a 14" pizza and then another half pizza. Now I can't even eat half. My stomach's grown since the day the diet finally ended, but it's a very slow pace. The day I finished, I tried pigging out - that was the idea. I had a lot of dumplings, fattening food, but I couldn't handle much. Before the diet I used to have 40 dumplings every day. That time I could only handle 11.

So the film's made you healthier.

Most definitely. Stronger, healthier. I can swim now and control my breathing. I have a deeper understanding of how my body and mind work together.

I know you spent a lot of time meditating with Mr Lee. What did that involve, and how did it benefit you?

Lots of focusing and relaxing our bodies and minds. You enter your cave and understand yourself better, you can fill yourself with light. By the end of it all you're in a perpetual state of meditation: things happen around you, not to you. On set I was being beaten up by everything but I was completely OK with it, as if I was sitting with a whirlwind around me. Just sitting there, and it's cool.

I wonder if he does that on other films, or if it was specific to this one because of your character's isolation.

I've met a couple of actors he's worked with and they gave me the sense that he goes deeper than what is considered normal. He told me once that his understanding of his actors, and theirs of him, is far deeper than what he can have with anybody else. Because he really allows you to come inside his mind. You see what he's trying to project and you become part of that picture.

the work

life of pi

Sharing the screen with Bengal tiger Richard Parker in the 2012 fantasy adventure

behind the scenes

From left: Mr Lee and Mr Sharma on the set of Life of Pi, 2011

the oscars 2013

Mr Sharma wore Emporio Armani at this year's Oscars, at which Life of Pi won four awards

He was giving you acting coaching too - by the time it came to shooting were you completely confident about it?

No, I didn't know if I could act yet. I feel as if Ang directed me right. I don't know who else can direct me right. That's my fear. We'll see.

This must have been an intense film to make, and in terms of acting you were on your own a lot. Did you have vivid dreams while you were making it?

I did. It was disturbing. There was a phase which I've termed the dark age. For me. For a month Ang told everybody not to talk to me, so I'd have complete isolation. I was just meditating on my own or going through this super crazy work-out. I was hungry, thirsty, extremely tired, awake. And my dreams would be very dark. I would wake up very disturbed. I would wake up feeling, Jesus Christ... I felt as if there was a problem with me. There was a dream about an ocean and a boat going in, the water was going down into an abyss, it was all around me. It really messed me up. It was as weird as hell. I can't get that image out of my head.

Do you get treated differently at home now?

Yes. I don't like it. I appreciate that people appreciate your work; it's nice to know they like it. But I don't like attention. At all.

You're in the wrong industry.

I know. It's one thing I'm just weirded out by. I can't deal with it, I'm extremely awkward. People coming up to me, it bothers me.

Is that one of the things that would put you off acting again?

Yeah. That is the thing. That is it. The idea of fame or recognition, I don't want that at all. I love acting because you discover billions of things about yourself, you feel so free, like a bird, but suddenly that bird gets caged. Because you're always hiding, in that sense.

If you were cast in another film but it meant spending three months in a wave tank again...

I'd do it. Totally do it. I would go through all that again, any day. Oh my God. It was all horribly amazing.

Life of Pi is available on 3D Blu-ray, Blu-ray and DVD from April 29 and on digital platforms from April 15.